Portable pneumatic impact tool

ABSTRACT

A tool comprises a casing accommodating a housing for axial movement therein. There is provided a main piston mounted in the casing for axially moving therewith. The main piston is received in a space in the housing which is in constant communication with a compressed air source. The compressed air pressure in said space results in the development of a force applied to the casing so as to urge it away from the housing. There is also provided a hammer piston moving in the housing. The distinguishing feature of the tool consists in the fact that there is provided, on the hammer piston, an additional piston received in said space. During the operation of the tool the housing and the hammer piston perform, under the action of compressed air, reciprocations in the antiphase relation therebetween so that the changes in the volume of said space caused by the reciprocations of the housing are compensated for by the reciprocations of the additional piston, whereby the pressure fluctuations of the compressed air in the space are reduced, thereby lowering vibration at the casing and handle. The tool may be alternatively made with the main piston mounted in the casing to move together with the housing.

Klushin et al.

July 1, 1975 PORTABLE PNEUMATIC IMPACT TOOL Inventors: NikolaiAlexandrovich Klushin,

ulitsa Narodnaya, 1, kv. 23; Petr Avramovich Maslakov, ulitsa Voskhod,7, kv. 42; Vladimir Petrovich Kotov, 9 Trikotazhny pereulok, 27, all ofNovosibirsk,

Primary ExaminerErnest R. Purser Assistant Examiner-Richard E. FavreauAttorney, Agent, or Firm-Holman & Stern [57] ABSTRACT A tool comprises acasing accommodating a housing for axial movement therein. There isprovided a main piston mounted in the casing for axially movingtherewith. The main piston is received in a space in the housing whichis in constant communication with a compressed air source. Thecompressed air pressure in said space results in the development of aforce applied to the casing so as to urge it away from the housing.There is also provided a hammer piston moving in the housing. Thedistinguishing feature of the tool consists in the fact that there isprovided, on the hammer piston, an additional piston received in saidspace. During the operation of the tool the housing and the hammerpiston perform, under the action of compressed air, reciprocations inthe antiphase relation therebetween so that the changes in the volume ofsaid space caused by the reciprocations of the housing are compensatedfor by the reciprocations of the additional piston, whereby the pressurefluctuations of the compressed air in the space are reduced, therebylowering vibration at the casing and handle. The tool may bealternatively made with the main piston mounted in the casing to movetogether with the housing.

8 Claims, 10 Drawing Figures PORTABLE PNEUMATIC IMPA CT TOUL The presentinvention relates to pneumatic impact tools, and more particularly toportable pneumatic tools to be used in the machine building, andespecially in the foundry for compacting moulding sand, as well in theconstruction and for municipal works for compacting soil, sand and thelike.

Known in the art is a pneumatic impact tool comprising a casingaccommodating a housing axially movable relative thereto, a pistonmounted in the casing and axially movable together with either casing orhousing, a space inside the housing or casing in constant communicationwith a compressed air source, said piston being received in said space,the air pressure in said space resulting in the development of a forceapplied to the casing so as to urge it away from the housing, a hammerpiston mounted in the housing and axially movable relative thereto,working chambers defined by the housing and the hammer piston, anair-distribution device pro viding the supply of compressed air into theworking chambers so as to impart reciprocations to the housing andhammer piston, whereby the hammer piston imparts useful blows.

The use of the casing in which the housing can move freely enables somereduction of the casing vibration transmitted to the operator hands.

However, as a result of the relative antiphase movement between thehammer piston and the housing, the latter performs longitudinaloscillations relative to the casing, whereby the volume of the spacecommunicated with a compressed air source is subjected to cyclicalfluctuations. As a result, the air pressure in the space is alsosubjected to cyclical fluctuations, whereby the force applied to thecasing varies so that there is still rather high vibration level on thecasing and handle. Vibration is transmitted, through the handle, to thehands of the operator thus endangering his health conditions. After acontinuous operation with such tool the operator is prone to theprofessional disease. In order to reduce pressure fluctuations in thespace communicated with a compressed air source, rather large volume ofthis space is required which is undesirable since in that case the sizeand weight of the tool are increased. Furthermore, such prior art toolhas considerable size and weight due to comparatively thick housingwalls which should accommodate passages for feeding compressed air fromthe air-distribution device into the working chambers.

Other attempts have been made to lower vibration at the handles of aportable pneumatic impact tool. Thus, known in the art is a pneumaticimpact tool, namely a tamper, comprising a handle with means providingthe supply of compressed air. Mounted coaxially with the handle are ahousing with a working member and a reaction member which are movablerelative to the handle. There are provided means for feeding compressedair into the space between the housing and the reaction member, and aspring mounted therebetween so as to impart reciprocations to thesemembers, whereby the working member imparts blows at the material beingcompacted. In this tool, compressed air and the spring do not generateany forces directed to displace the handle so that no vibration ariseson the handle. However, during the operation, the handle weight isapplied to the operator since he should hold the handle suspended whichresults in a rapid fatigue of the operator.

In another embodiment of such prior art tool this disadvantage iseliminated by applying a thrust force between the handle and thehousing. The handle has a chamber communicating with a compressed airsource. This chamber receives a sliding piston connected to the housingso that under the compressed air pressure there are developed, in thechamber, a force applied to the handle and a force applied to thepiston, whereby the housing and the handle tend to move apart.

However, during the operation of this tool the housing, which is at thesame time the hammer member, performs reciprocations, and the pistonalso performs oscillations in said chamber axially relative to itsintermediate position. The oscillations of the piston cause fluctuationsin the volume of said chamber, and hence compressed air pressurefluctuations therein, thereby resulting in unhealthy vibration at thehandle.

In addition, in such a tool the amount of displacement of the housingwith the working member is comparatively small because it is difficultto make a lightweight housing. This hampers the employment of such toolsin compacting thick layers of materials. The amount of said displacementcould be increased by using a heavier reaction member which is alsoundesirable.

The labor conditions could be improved by stabilizing the magnitude ofthe forces applied to the handle so as to lower unhealthy vibration,with the provision being made to eliminate the transmission of thehandle weight to the hands of the operator.

The attempts have been made in this direction by the provision of aportable pneumatic impact tool comprising a handle and a housingaccommodated therein and capable of performing a limited axial movementrelative thereto, a hammer piston being axially movable in the housingtogether with means for imparting reciprocations thereto, whereby thehammer piston accomplishes a useful work by imparting blows. Spaces inconstant communication with a compressed air source are formed in thehousing. lPistons are fixed to the handle and received in said space.The housing vibrates rel ative to the handle during the operation, andthe piston enters and leaves said space. In order to maintain a constantpressure in the space, that is to lower vibration at the handle, thereare provided means for feeding compressed air thereinto at the moment,where the volume of said space increases and the pressure thereindecreases, as well as means for discharging the compressed air from thespace into atmosphere, where the volume of the space decreases and thepressure therein increases. Such tool has, however, an elevated compressed air consumption due to the air exhaust from said space intoatmosphere. The exhaust of compressed air into atmosphere results inaerodynamic noise which is also undesirable. In winter, means used fordischarging an excess air into atmosphere are iced thus resulting introubles and even failures in the operation of the means providing theapplication of a constant force to the handle, whereby vibration isincreased. in addition, this tool is complicated.

It is an object of the invention to provide a portable pneumatic impacttool having lower vibration at the tool handle.

Another object of the invention is to provide a pneumatic tool havingsmaller size and weight with the same capacity.

Still another object of the invention is to provide a pneumatic toolhaving reduced air consumption.

These and other objects are accomplished by the provision of a pneumaticimpact tool comprising a casing having therein a housing axially movablerelative thereto, a mainpiston mounted in the casing and axially movabletogether with either casing or housing, a space defined inside thecasing or housing in constant communication with a compressed airsource, said piston being received in said space, the compressed airpressure in said space resulting in the development of a force appliedto the casing so as to urge it away from the housing, a hammer pistonaxially movable in the housing, working chambers defined by the housingand the hammer piston, an air-distribution device providing the supplyof compressed air into the working chambers so as to impartreciprocations to the housing and hammer piston, whereby the hammerpiston imparts useful blows, wherein, according to the invention, thereis provided an additional piston received in said space and drive meansfor imparting reciprocations to the additional piston substantially inthe antiphase relation to the reciprocations of the housing, thevariation of the volume of said space caused by said reciprocations ofthe housing being substantially compensated for by said reciprocationsof the additional piston, whereby pressure fluctuations of thecompressed air in said space are reduced and the magnitude of the forceapplied to the casing is thereby maintained constant so as to lower itsvibration.

It is advantageous that the additional piston constitutea part of thehammer piston.

This embodiment of the piston simplifies the provision of the drive ofthe additional piston since the hammer piston reciprocates substantiallyin the antiphase relation to the reciprocations of the housing.

The additional piston is preferably provided with a passage having oneend communicated with a compressed airsource and the other endcommunicated with the air-distribution device.

This permits to increase the volume of said space, whereby pressurefluctuations of the compressed air therein are reduced, and hencevibration at the casing (handle) is lowered. In addition, this enablesthe reduction of the weight and size of the tool.

The air-distribution device is preferably arranged in the hammer piston,whereby the weight and size of the tool are also reduced.

The invention provides a pneumatic impact tool having lower vibration atthe tool handle and smaller weight and size with the same capacity,while unproductive air consumption is eliminated.

The invention will now be described in greater details with reference tospecific embodiments thereof illustratedin the accompanying drawings, inwhich:

FIG. 1 shows a longitudinal section of a portable pneumatic impact toolaccording to the invention illustrated to the section a'--a';

FIG. 1 is the continuation of FIG. 1 from the section a-a' to thesection aa" and down;

FIG. 1" shows a section from section aa" to the bottom of the tool;

FIG. 2 is a partial section taken along the line IIII in FIG. 1';

FIG. 3 is a partial section taken along the line III-III in FIG. 1;

FIG. 4 schematically shows a portable pneumatic impact tool according tothe invention, partially in section, illustrating the lowermost positionof the hammer piston during theoperation;

FIG. 5 is Ditto, with the uppermost position of the hammer piston duringthe operation;

FIG. 6 shows the hammer piston in the position adjacent to theair-distribution device;

FIG. 7 shows a longitudinal section of another embodiment of theportable pneumatic impact tool according to the invention illustrated tothe section b-b', with the main piston connected to the housing;

FIG. 7 is the continuation of FIG. 7 from the section b -b and down.

In the description of the embodiments of the invention illustrated inthe accompanying drawings specific narrow terms are used for the sake ofclarity. It should, however, be noted that each term covers allequivalent elements having similar functions and applicable in solvingsimilar problems.

A portable pneumatic impact tool shown in FIGS. 1, l, 1", 2, 3 and 6 isa tamper and comprises a-casing 1 which consists of a handle 2, a tube 3screwed thereto and a tube 4 which is, in turn, screwed on the tube 3.The casing 1 accommodates a hollow housing 5, which is axially movablewithin certain limits relative thereto, and a hammer piston 6 which isalso axially movable within certain limits in the housing 5 and has arod 7 to which there is attached a working tool (shoe) 8.

The handle 2 is provided with a triggering device 9 of a known designwhich is actuated by pressing down a lever 10 pivotably fixed to thehandle 2 by means of a pivot 11. In addition, the handle 2 is providedwith a passage 12 communicated with a through passage 13 of a mainpiston 14. The piston 14 hasa shoulder 15. A nut 16 is screwed into thelower end of the handle 2, and the shoulder 15 of the piston 14 bearsagainst the nut thereby preventing the piston from falling out of thehandle. A sealing bush 17 made of rubber or other sealing material ismounted between the piston 14- and the handle 2, and in order to ensuresatisfactory sealing, the bush 17 is urged by the nut 16 through theshoulder 15 of the piston 14. A radial space is provided between the nut16 and the piston 14, as well as between the piston 14 and the handle 2so that the piston 14 may be radially displaced by a certain amount. Thehandle 2 has a passage 18 and an internal thread 19 at the upper endthereof for connection of the tool to a compressed air source (notshown) by known means. The passage 18 can communicate with the passage12 through the air-distribution device 9. Chambers 21 and 22 are definedbetween the housing 5 and the hammer piston 6. A barrel 20 constitutesthe main part of the housing 5. The upper end of the. barrel 20 receivesa tube 23 which has a shoulder 24 bearing against the barrel 20 and issecured to the barrel by means of a sleeve 25 urging the shoulderagainst the barrel. The sleeve 25, in its turn, is secured to the barrel20 by means of a threaded connection. In order to eliminate air leakagethrough this thread, it is sealed with a special adhesive compound,paint or the like (not shown). Where the thread is of a sufficientlength, the sealing is ensured by the threaded connection itself, andthe above-mentioned sealing materials may be dispensed with. The sleeve25 functions also as guide for the casing 1. A chamber 26 is definedbetween the sleeve 25 and the barrel 20 which communicates with thechamber 21 through openings 27 made in the upper part of the barrel 20.In order to provide the discharge of exhaust air from the chambers 21and 22, exhaust ports 28 are made in the barrel 20. An aperture 29communicated with the exhaust ports 28 and with atmosphere is providedbetween the barrel and the tube 4 of the casing 1 so as to direct theexhaust air downwards to disperse it in the atmosphere. The lower partof the barrel 20 is internally provided with a counterbore 30 de finingan annular face 31 of the barrel. A guide bush 32 having a centralopening for loosely mounting the rod 7 bears against this face. A seal33 is located beneath the guide bush 32 to prevent air from leaking intoatmosphere from the space 22 through the gaps between the guide bush 32and the rod 7, as well as between the guide bush 32 and the barrel 20.The seal 33 is made of felt or the like material and is urged againstthe guide bush 32 by means of a sleeve 34, which is, in turn, urged by anut 35 screwed on the barrel 20 and having a central bore for looselymounting the rod 7. To compensate for the wear of the seal 32, the nut35 can be screwed further on the barrel 20 to compress the seal 33,thereby prolonging its service life.

The hammer piston 6 is made composite. It includes the rod 7 and a shank36 screwed therein. These elements are locked against unscrewing bymeans of a pin 37. An additional piston 38 is mounted in the hammerpiston 6 which is made integral with the shank 36 so that the hammerpiston 6 is concurrently used as drive means of the additional piston38. It is known that during the operation of the tool the hammer pistonmoves substantially in the antiphase relation to the reciprocations ofthe housing 5, and therefore this embodiment of the hammer piston 6permits to simplify the drive of the additional piston 38. In order toimpart reciprocations to the additional piston 38 in the antiphaserelation to the reciprocations of the housing 5, other drive means maybe used which can ensure the achievement of the same result.

The additional piston 38 is provided with a passage 39 open at the upperend. The lower end of the passage 39 communicates with anair-distribution device 40 of a conventional type having a valve member40a with the upper face 41 and the lower face 42, and a seat 43 with theupper face 44 and the lower face 45 which are adapted to cooperate withthe faces 41 and 42 of the valve member 40a, respectively. The hammerpiston 6 has passages 46 and 47 terminating at the respective faces 44and 45 of the valve seat 43. The passages 46 communicate with thechamber 21, and the passages 47 communicate with the chamber 22 throughpassages 48 and 49 made in the rod 7 0f the hammer piston 6. A permanentgap is provided between the faces 44 and 45 of the valve seat 43 and therespective faces 41 and 42 of the valve member 40a, since the thicknessof the valve member 40a is smaller than the width of the valve seat 43.Therefore, the valve member 40a can perform a limited movement in thevalve seat 43. The chambers 21 and 22 can communicate with the passage39 through the passages 46, 47 and the gap in the valve seat 43, thepassage 39 being connected to the chamber 21 when the valve member 40ais in the lowermost position, and with the chamber 22 when the valvemember is in the uppermost position.

A central bore having portions of different diameter is provided in thetube 23. The portion of the bore having a larger diameter is made in theupper part of the tube 23, and the portion ofa smaller diameter in thelower part thereof. The piston 14 is received for reciprocations in theupper part of the bore of the tube 23, the piston 14 being slidablysealed in said tube 23. The additional piston 38 is received forreciprocations in the bore in the lower part of the tube 23, theadditional piston being slidably sealed in the tube 23.

A nut member 50 is screwed on the upper part of the tube 23, and arubber ring 51 is secured to the nut member (e.g., with an adhesivecompound). A rubber ring 52 is secured to the lower part of the tube 23.The rings 51 and 52 are used as resilient stops limiting thedisplacement of the housing 5 in the casing 1. The sleeve 25, nut 32,guide bush 32, sleeve 34, seal 33, tube 23, nut member 50 and the rings51 and 52 move together with the barrel 20 and form the housing 5 incombination therewith. The casing 1 may bear against the rings 51 and 52by means of its shoulder 53 arranged to provide a space relative to thetube 23.

The portions of the bore of the tube 23 form therebetween a space 54communicated with a compressed air source through the passage 13 of thepiston 14, the passage 12 of the handle 2, the triggering device 9 andthe passage 18. The above-described means used for the slidable sealingof the pistons 14 and 38 prevents air from leaking from the space 54.

An opening 55 is made in the tube 4 of the casing 1 to communicate thespace 56 inside the casing with atmosphere thereby maintainingatmospheric pressure in the space 56.

All component parts of the tool interconnected by means of thread arelocked by known means.

For better illustration of the operation of the tool, the latter isschematically shown in FIGS. 4 and 5. In FIGS. 4 and 5 the referencenumerals indicating similar parts of the tool are identical to thoseused in FIGS. 1, 1 1", 2, 3 and 6 showing the same tool which isillustrated in the FIGS. 4 and 5 in somewhat simplified manner. Thus,instead of showing the barrel and the elements secured thereto, there isillustrated the housing as an integral piece, the passages 48 and 49 inthe hammer piston 6 are not shown, while the passages 47 arecommunicated directly with the chamber 22, and so on. Thesesimplifications are not critical for the explanation which will be givenhereinbelow.

FIGS. 7 and 7' show another embodiment of the tool comprising a casing57 consisting of a handle 58, a tube 59 screwed thereon and a tube 60screwed in the tube 59. The handle 58 is constructed similarly with thehandle 2 shown in FIG. 1. A passage 61 made in the handle 58communicates with a compressed air source through a triggering device ofa conventional type (not shown). A housing 62 similar to the housing 5shown in FIGS. 1, 1, 1" is accommodated in the casing 57 axially movablerelative thereto within certain limits, and a main piston 63 is securedto the barrel 20 of the housing 62 by means of the sleeve 25 screwed onthe barrel 20.

The piston 63 is made hollow and defines, together with the casing 57, aspace 64 communicated with a compressed air source through the passage61 and the triggering device (not shown). A nut 65 is screwed on theupper part of the piston 63, and a rubber ring 66 is secured to the nut65. A rubber ring 67 is secured to the lower part of the piston 63. Thecasing 57 has a reduced portion 68 having a bore receiving the slidablyand sealingly mounted piston 63. In addition, the re- 7 duced portion 68limits the movement of the housing 62 relative to the casing 57 by meansof the rings 66 and 67. I

An opening 69 is made in the tube 60 and is communicated with atmosphereand witha space 70iriside the tube 60, whereby atmospheric pressure ismaintained in the space 70. Therefore, the function of the opening 69 issimilar to that of the opening 55 in FIGS. 1', 4 and 5.

The hammerpiston 6 is mounted for a limited axial movement in thehousing 62, the construction of the hammer piston being identical withthat described above. The additional piston 38 with the passage 39therein constitutes a part of the hammer piston. The additional piston38 is received through the central bore in the lower part of the piston63 for reciprocation in the space 64. i

The component parts of the tool shown in FIGS. 7 and 7' are mainlyindicated using the same reference numerals as for the components partsof the tool shown in FIGS. 1, 1', 1", 2, 3, 4, and 6 performing similarfunctions. i g

The pneumatic tool shown in FIGS. 1, 1, 1", 2, 3, 4, 5 and 6 functionsas follows. I

The initial position is shown in FIGS. 1, 1' and 1", and in thisposition of the tool the hammer piston 6 is in such a position, that thechamber 21 communicates with atmosphere through the exhaust ports 28 andthe aperture 29. This position corresponds to theinstant of thedeliveryof a blow by the hammer piston 6 at the material being compacted(not shown), and the valve member 40a is in its lowermost position sothat its lower face 42 is in contact with the lower face 45 of the valveseat 43 to close the passages 47 of the hammer piston 6. Between theupper face 41 of the valve member 40a and the upper face 44 of the valveseat 43 there is a gap communicating the passages 46 of the hammerpiston 6 with the passage 39 of the additional piston 38. The housing 5is in the position at which the portion 53 of the casing 1 is locatedbetween the rings 51 and 52 and somewhat closer to the ring 52. Thelever 10 of the handle 2 is free so that the triggering device 9 isclosed.

When the operator presses down the lever 10, the triggering device 9 isactuated, and the compressed air is fed through the passage 12 of thehandle 2 and the passage 13 of the piston 14 into the space 54 of thetube 23. During the operation, the space 54 is under the pressure ofcompressed air which is about equal to the pressurein the air line.Thus, a substantially constant upwardly directed force F, is applied tothe casing 1 whose magnitude is equal to the product of the total areaof the cross-section of the piston 14 (including the clear area of thepassage 13) by the air pressure in the space 54. In order to improve thelabor conditions, the

' magnitude of this force F is preferably selected to be to the productof the air pressure in the space 54 by the area of a ring surface whichgiven by the difference between the cross-sectional area of the piston14 and the total cross-sectional area of the additional piston 38(including the clear area of the passage 39). The mag- 'the upper face41 of the valve member a and the upper face 44 of the valve seat 43 isthe smallest one along the entire air duct of the tool, and for thatreason the air velocity at that point is at its maximum, while thestatic head is at its minimum.

At the same time, the compressed air leaks through microscopic gapswhich are always available between the lower face 42 of the valve member40a and the lower face 450 f the valve seat 43. The pressure acting uponthe face 42 of the valve member 40a is substantially equal to the airline pressure, and this pressure is, of course, greater than thepressure applied to the face 41 thereof, whereby the valve member 40awill be substantially instantaneously shifted upwards to take theposition shown in FIG. 4. In this position the face 41 of the valvemember 40a is in contact with the face 44 of the valve seat 43 toshut-off the passages 46 of the hammer piston. Compressed air flow intothe chamber 21 is interrupted,and the air begins to flow into thechamber 22 through the gap formed between the lower face 42 of the valvemember 40a and the lower face 45 of the valve seat 43, and the passages47, 48, 49 in FIGS. 1 and 6 or through passages 47 in FIGS. 4 and 5.

The pressure in the chamber 22 starts increasing and acts upon thehammer piston 6 and the guide bush 32, and thereby upon the housing 5 asa whole. When the air pressure force applied to the hammer piston 6 fromthe side of the chamber 22 will overcome the force F and the weight ofthe hammer piston 6, the hammer hammer piston 6 the exhaust ports 28 areopened, and

the chamber 22 is communicated with atmosphere through these exhaustports and the aperture 29. The exhaust of the air from the chamber 22into atmosphere begins, and the air pressure therein will startdecreasing so as to become equal to the atmospheric one.

.The pressure in the gap between the lower face 42 of the valve member40a and the lower face 45 of the valve seat 43 alsodecreases. The hammerpiston 6 and the housing 5 continue to move towards each other so thatthe pressure in the chamber 21 will grow higher. At a certain point thepressure applied to the upper face 41 of the valve member 40a willovercome the pressure applied to its lower face 42, and the valve member40a will be shifted into the lowermost position nitude of this force isselected depending on the parameters of the tool. Approximately constantforcefiF equal to the product of thev air. pressure in the space '54 sothat the compressed air will enter the chamber 21 from the passage 39through the gap between the upper face 41 of the valve member 40b andthe upper face 44 g of the valve seat 43 and through the passages 46.The

chamber 21 communicates with the chamber 26 through the openings 27. Thechamber 26 constitures something like the additional volume of thechamber 21 thus contributing to more gradual pressure growth. Thiscauses an increase in the stroke of the hammer piston 6 relative to thehousing which is favourable for the energy performance of the tool. Themovement of the housing 5 is slowed down under the action of thepressure force of the air compressed in the chamber 2ll and enteringsaid chamber 21 from the passages 46, and a certain space will remainbetween the ring 511 moving together with the housing 5 and the portion53 of the casing 1. Under the action of the pressure force in thechamber 21, under the own weight of the hammer piston 6 and under theaction of the force F the hammer piston 6 will be slowed downapproximately at the same point, when its enalrged portion has not yetreached the tube 23.

During all that time, the additional piston 38, which constitutes a partof the hammer piston 6 and moves upwards together therewith, telescopesinto the space 54, the volume of the space 54 decreasing by the amountequal to the product of the total cross-sectional area of the additionalpiston 38 by the stroke of the hammer piston 6 relative to the housing5. However, since the housing 5, during that time, was moving in thedirection opposite to the direction of movement of the hammer piston 6,that is downwards so that the housing 5 telescoped from the casing 1,the volume of the space 54 has been increased by the amount equal to theproduct of the total cross-sectional area of the piston 14 secured tothe handle 2 by the stroke of the housing 5 relative to the casing ll. Achange in the volume of the space 54 is equal to the difference betweenthe increments of its volume due to the telescoping of the additionalpiston 38 into the space and the telescoping of the housing 5 from thecasing l to whose handle 2 there is attached the piston 14. With anappropriate selection of the total cross-sectional areas of the pistons14 and 38 and the strokes of the hammer piston 6 relative to the housing5 and of the housing 5 relative to the casing l, the change in thevolume of the space 54 may be substantially reduced to zero. it isobvious that in that case the air pressure in the space 54 remainspractically unchanged, and therefore, the force F, applied to the casing1 is also constant so that the casing l and the handle 2 are notsubjected to any excitation, that is they will not vibrate.

After the housing 5 has been slowed down, it starts moving upwards underthe action of the pressure force in the chamber 21 overcoming the forceF and the own weight of the housing 5. After the hammer piston has beenslowed down, it starts moving downwards under the action of the pressureforce in the chamber 21, its own weight and the force F During thedownward movement of the hammer piston 6 and during the upward movementof the housing 5 the exhaust ports 28 are closed, and the compression ofthe air entrapped in the chamber 22 begins so that the pressure in thischamber increases. During further upward movement of the housing 5 andthe downward movement of the hammer piston 6 the exhaust ports 28 areopened, and the exhaust air will leave the chamber 2ll into atmospherethrough these ports and through the aperture 29 so that the pressure inthe chamber 211 abruptly drops. The pressure will be also decreased inthe passages 46 and in the gap between the upper face 4ll of the valvemember 44 a and the upper face 44 of the valve seat 43. When the airpressure applied to the lower face 42 of the valve member 4th willovercome the pressure acting upon its upper face 42, the valve member isshifted to the uppermost position so as to shut-off the passages 46 withits face 411, and the compressed air flow into the chamber 211 will beinterrupted. The compressed air will begin to flow through the gapbetween the lower face 42 of the valve member 40a and the lower face ofthe valve seat 43 and through the now open passages 47 into the chamber22.

The hammer piston 6 will deliver, with the working tool (shoe) 8, a blowat the material being compacted (not shown) overcoming the pressureforce in the chamber 22. The relative position of the component parts ofthe tool at the instant of the delivery of a blow is schematically shownin FIG. 5. After the delivery of a blow, the hammer piston 6 will startmoving upwards under the action of the pressure of compressed air in thechamber 22, and partially due to the rebound from the material beingcompacted, overcoming its own weight and the force F which ispermanently applied to the hammer piston 6 in the downward direction.The housing 5, under the action of the pressure of the compressed air inthe chamber 22, as well as under its own weight and the force F appliedthereto upwards from the space 54, will be also stopped approximately atthe instant of blow and will start moving downwards under the action ofthe above-mentioned forces. At the instant of the immobilization of thehousing 5 a space still remains between the portion 53 of the casing lwith the handle and the housing ring 52. Then the cycle of operation isrepeated.

During the period of the upward movement of the housing 5 and thedownward movement of the piston 6, due to the telescoping of theadditional piston 38 from the space 54, the volume of this spaceincreases by the amount equal to the product of the total crosssectionalarea of the additional piston 35 by the stroke of the hammer piston 6relative to the housing 5. At the same time, due to the telescoping ofthe housing 5 into the casing l, the volume of the space 54 decreases bythe amount equal to the product of the total crosssectional area of thepiston 14 by the stroke of the housing 5 relative to the casing t. Thisdecrease in the volume of the space 54 is compensated for by the increase in its volume due to the telescoping of the additional piston 35therefrom, whereby the volume of the space 54 remains practicallyunchanged which, as it was mentioned above, contributes to the loweringof vibration at the casing l and handle 2.

During the operation of the tool the volume of the space 56 iscyclically varied, but since this space communicates through the openingwith atmosphere, a constant pressure is maintained therein which isequal to the atmospheric one, and variations of this volume do notresult in any increase in vibration of the casing l and the handle 2.

Under steady operating conditions, the housing 5, while reciprocating,oscillates about a certain point so that it does not reach the portion53 of the casing 53 with its rings 51 and 52., Random hitting of one ofthe rings 51, 52 against the portion 53 with the resulting vibration atthe casing l and the handle 2 may be readily eliminated by moving theentire casing 1 up or down.

Therefore, during the operation of the impact tool according to theinvention, due to the movement of the 1 1 piston 14 and additionalpiston 38 in the space 54, the

volume of this space 54 remains substantially unchanged. The constantvolume of the space 54 contributes to the maintenance of a constant airpressure therein so as to ensure a constant force applied during all thetime to the casing l and handle 2. The absence of the force fluctuationresults in the absence of vibration at the casing 1 and the handle 2held by the operator.

The operation of the portable pneumatic tool, namely of the tamper shownin FIGS. 7 and 7 is practically similar to the operation of the toolshown in FIGS. 1, 1', l, 2, 3, 4, and 6.

After the triggering device (not shown) is actuated, compressed airenters the space 64 through the passage 61. During the operation thespace 64 is permanently under the pressure of compressed air. Therefore,substantially constant force F, is applied upwards to the casing 57, themagnitude of this force being equal to the product of the totalcross-sectional area of the piston 63 at any section intermediate theportion 68 and the ring 66 or 67 (including the cross-sectional area ofthe space 64 at that point which is enclosed by the piston 63) by theair pressure in the space 64.

A substantially constant force F which is equal to the force F, and isdirected downwards, is applied to the piston 63, and thereby to thehousing 62 as a whole.

A substantially constant force F is applied downwards to the hammerpiston 6, which is equal to the product of the cross-sectional area ofthe additional piston 38 by the air pressure in the space 64.

The compressed air is fed from the space 64 through the passage 39 tothe air-distribution device 40 and is fed thereby alternately into thechambers 21 and 22 as it was described with reference to FIGS. 1, 1', 12, 3, 4, 5 and 6, whereby the hammer piston 6 and the housing 62 performreciprocations, the hammer piston 6 moving substantially in theantiphase relation to the reciprocations of the housing 62 anddelivering useful blows at the material being compacted (not shown).

As a result of the above-described movement of the housing 62, thepiston 63 moving together therewith will alternately telescope into andfrom the space 64 to respectively reduce and increase the volume of saidspace. At the same time, the additional piston 38, which constitutes apart of the hammer piston 6 and moves in the antiphase relation to thereciprocations of the housing 62, and hence of the piston 63,alternately telescopes from and into the space 64 to respectivelyincrease and reduce the volume of said space. The cross-sectional areaof the piston 63, the stroke of the housing 62 relative to the casing 57and the crosssectional area of the additional piston 38 and the strokeof the hammer piston 6 relative to the housing 62 are selected in such amanner that the decrease in the volume of the space 64 due to thetelescoping of the piston 63 thereinto is substantially compensated forby the increase in the volume of the space 64 due to the telescopingthereform of the additional piston 38, while the increase in the volumeof the space 64 due to the telescoping of the piston 63 therefrom issubstantially compensated for by the decrease in the volume of the space64 due to the telescoping of the additional piston 38 thereinto, wherebythe volume of the space 64 remains substantially unchanged.

Due to the constant volume of the space 64, the air pressure therein isconstant, and therefore, the force F applied to the casing also remainsunchanged, so that the casing and the handle 58 are not subjected to anyexcitation, that is theydo not vibrate.

Under steady operating conditions the housing 62, while receprocating,performs oscillations about a certain point so that its rings 66 and 67do not reach the portion 68. Random hitting of one of the rings 66, 67against the portion 68 and the resulting vibration of the casing 57 andthe handle 58 are readily eliminated by moving the entire casing 57 upor down.

It should be noted that the embodiment of the invention illustrated inthe accompanying drawings and described hereinabove represent anillustrative example only and various modifications may be made asregards the shape, dimensions and arrangement of certain elements. Thus,the components parts illustrated in the drawings and described above maybe replaced by their equivalents, the position of some elements may bechanged, and certain elements of the invention may be used independentlywithout departure from the spirit and scope of the invention as definedin the appended claims.

An experimental pneumatic tamper constructed in accordance with theinvention has been tested by compacting various materials, such asmoulding sand, sand, loose soil and the like under divers conditions incomparison with known tampers. The tests have shown that the vibrationlevel at the casing and handle of the tamper according to the inventionwas substantially lower as compared with the known tampers with asmaller weight of the tamper and other parameters being the same.

What is claimed is:

l. A portable pneumatic impact tool comprising: a casing; a housing insaid casing axially movable relative thereto and having a space inconstant communication with a compressed air source; a main pistonmounted in said casing and received in the space of said housing foraxial movement together with said casing relative to said housing, thecompressed air pressure in the space of said housing resulting in thedevelopment of a force applied to said casing so as to urge it away fromsaid housing; a hammer piston mounted for axial movement in said housingfor imparting useful blows; said housing and said hammer piston definingworking chambers which are alternately communicated with a compressedair source and atmosphere; means for alternately feeding compressed airinto said working chambers for thereby imparting reciprocations to saidhousing and said hammer piston, whereby said hammer piston impartsuseful blows; an additional piston; drive means for impartingreciprocations to said additional piston substantially in the antiphaserelation to the reciprocations of said housing; said additional pistonbeing received in the space of said housing during the reciprocations sothat variations in the volume of the space of said housing caused by thereciprocation of said housing are substantially compensated for by thereciprocations of said additional piston, whereby the volume of thespace of said housing remains substantially unchanged, and hence thepressure fluctuations "of the compressed air in the space of saidhousing are reduced, whereby the force applied to said casing ismaintained constant and vibration of said casing is lowered.

2. A pneumatic tool according to claim ll, wherein said additionalpiston constitutes a part of said hammer piston.

3. A pneumatic tool according to claim 1, wherein said means foralternately feeding compressed air into said working chambers comprisesa valve-type airdistribution device accommodated in said hammer pistonand communicated with a compressed air source.

4. A pneumatic tool according to claim 3, wherein said additional pistonis provided with a passage having one end in permanent communicationwith a compressed air source and the other end in permanentcommunication with said air-distribution device.

5. A pneumatic impact tool comprising: a casing having a space inconstant communication with a compressed air source; a housing axiallymovable in said casing; a main piston mounted in said casing andreceived in the space of said casing for axial movement together withsaid housing relative to said casing, the compressed air pressure in thespace of said casing resulting in the development of a force applied tosaid casing so as to urge it away from said housing; a hammer pistonmounted for axial movement in said housing for imparting useful blows;said housing and said hammer piston defining working chambers which arealter nately communicated with a compressed air source and atmosphere;means for alternately feeding compressed air into said working chambersfor thereby imparting reciprocations to said housing and said hammerpiston, whereby said hammer piston imparts useful blows; an

additional piston; drive means for imparting reciprocations to saidadditional piston substantially in the antiphase relation to thereciprocations of said housing; said additional piston being received inthe space of said casing during the reciprocations so that variations inthe volume of the space of said casing caused by the reciprocations ofsaid housing are substantially compensated for by the reciprocations ofsaid additional piston, whereby the volume of the space of said casingremains substantially unchanged, and hence the pressure fluctuations ofthe compressed air in the space of said casing are reduced, whereby theforce applied to said casing is maintained constant and vibration ofsaid casing is lowered.

6. A pneumatic tool according to claim 5, wherein said additional pistonconstitutes a part of said hammer piston.

'7. A pneumatic tool according to claim 5, wherein said means foralternately feeding compressed air into said working chambers comprisesa valve-type airdistribution device accommodated in said hammer pistonand is communicated with a compressed air source.

8. A pneumatic tool according to claim 7, wherein said additional pistonis provided with a passage having one end communicated with the spacewhich is permanently communicated with a compressed air source, and theother end communicated with said airdistribution device.

l= =l l l=

1. A portable pneumatic impact tool comprising: a casing; a housing insaid casing axially movable relative thereto and having a space inconstant communication with a compressed air source; a main pistonmounted in said casing and received in the space of said housing foraxial movement together with said casing relative to said housing, thecompressed air pressure in the space of said housing resulting in thedevelopment of a force applied to said casing so as to urge it away fromsaid housing; a hammer piston mounted for axial movement in said housingfor imparting useful blows; said housing and said hammer piston definingworking chambers which are alternately communicated with a compressedair source and atmosphere; means for alternately feeding compressed airinto said working chambers for thereby imparting reciprocations to saidhousing and said hammer piston, whereby said hammer piston impartsuseful blows; an additional piston; drive means for impartingreciprocations to said additional piston substantially in the antiphaserelation to the reciprocations of said housing; said additional pistonbeing received in the space of said housing during the reciprocations sothat variations in the volume of the space of said housing caused by thereciprocation of said housing are substantially compensated for by thereciprocations of said additional piston, whereby the volume of thespace of said housing remains substantially unchanged, and hence thepressure fluctuations of the compressed air in the space of said housingare reduced, whereby the force applied to said casing is maintainedconstant and vibration of said casing is lowered.
 2. A pneumatic toolaccording to claim 1, wherein said additional piston constitutes a partof said hammer piston.
 3. A pNeumatic tool according to claim 1, whereinsaid means for alternately feeding compressed air into said workingchambers comprises a valve-type air-distribution device accommodated insaid hammer piston and communicated with a compressed air source.
 4. Apneumatic tool according to claim 3, wherein said additional piston isprovided with a passage having one end in permanent communication with acompressed air source and the other end in permanent communication withsaid air-distribution device.
 5. A pneumatic impact tool comprising: acasing having a space in constant communication with a compressed airsource; a housing axially movable in said casing; a main piston mountedin said casing and received in the space of said casing for axialmovement together with said housing relative to said casing, thecompressed air pressure in the space of said casing resulting in thedevelopment of a force applied to said casing so as to urge it away fromsaid housing; a hammer piston mounted for axial movement in said housingfor imparting useful blows; said housing and said hammer piston definingworking chambers which are alternately communicated with a compressedair source and atmosphere; means for alternately feeding compressed airinto said working chambers for thereby imparting reciprocations to saidhousing and said hammer piston, whereby said hammer piston impartsuseful blows; an additional piston; drive means for impartingreciprocations to said additional piston substantially in the antiphaserelation to the reciprocations of said housing; said additional pistonbeing received in the space of said casing during the reciprocations sothat variations in the volume of the space of said casing caused by thereciprocations of said housing are substantially compensated for by thereciprocations of said additional piston, whereby the volume of thespace of said casing remains substantially unchanged, and hence thepressure fluctuations of the compressed air in the space of said casingare reduced, whereby the force applied to said casing is maintainedconstant and vibration of said casing is lowered.
 6. A pneumatic toolaccording to claim 5, wherein said additional piston constitutes a partof said hammer piston.
 7. A pneumatic tool according to claim 5, whereinsaid means for alternately feeding compressed air into said workingchambers comprises a valve-type air-distribution device accommodated insaid hammer piston and is communicated with a compressed air source. 8.A pneumatic tool according to claim 7, wherein said additional piston isprovided with a passage having one end communicated with the space whichis permanently communicated with a compressed air source, and the otherend communicated with said air-distribution device.